How a two-step rev limiter works

How a two-step rev limiter works

A rev limiter is there for your benefit. Without it, you'd be facing down a potential busted engine and trickier launches, especially in higher horsepower vehicles. If you have a vehicle with a launch control mode, then you have a car fitted with a two-step rev limiter. One step is designed to help you get off the line as quickly and efficiently as possible, while the other step is there to protect your precious spinning engine parts. Jason Fenske from Engineering Explained is here to tell you how it all works.

With the first rev limiter, the computer tells the engine to hold at a certain pre-set rev limit. This is designed to minimize wheel spin and get you moving down the road quickly from a stop. It's launch control, and it's a ton of fun. The second rev limiter sits at or just past the redline rev location on your tachometer. It prevents the engine from spinning faster than its given upper limit, as doing so will lead to a high potential for internal damage.

So how does this all work? There are usually two ways in which your car's computer limits revs. One version cuts fuel while the other cuts back on the spark. When you reduce either of those, you limit the level of combustion taking place inside the engine and therefore limit what the engine can produce in terms of power and how fast it can spin.

With regard to fuel, the engine will either receive a leaner air-fuel mixture or it will simply cut off the flow of fuel into the engine.

When the computer limits revs through a spark reduction, it does so by altering the spark timing or by cutting the spark. When this happens, unburnt fuel flows through the engine and enters the exhaust system where it creates those popping and crackling sounds that are so popular on current sporty cars.

By limiting its revs, either on the low end for launches or the high end for engine protection, your car is working to make the driving experience better. You'll have more fun laying down efficient launches, and even more fun keeping your engine safe and away from expensive repair bills caused by a high-rev event.